Modified atmosphere packaging (MAP) is widely practiced in the food packaging industry as a way of reducing spoilage of produce and increasing shelf life. MAP typically comprises modifying the composition of the gas that is present alongside food product in a food container so that it is different from the standard atmospheric composition in a way which maximises the longevity of the food product. This will typically involve increases and decreases of the proportion of oxygen, nitrogen and/or carbon dioxide in the atmosphere within food packages.
When food is packaged using modified atmosphere packaging, any incomplete sealing of the packaging reduces or nullifies entirely the increased shelf life provided by the MAP process as the atmosphere within the package is allowed to return to standard atmospheric composition.
In order to try to identify containers which have a breach, i.e. an opening into the package which renders them incompletely sealed, packages are mechanically tested, typically in-line. Mechanical testing typically comprises mechanically squeezing the container and identifying an expected response as the pressure within the sealed package increases and the package resists the mechanically squeezing. Such methods of mechanically testing packages are typically very slow, which can limit the maximum production speed, or require many separate lanes to keep up with faster packaging systems. Such methods may also have limited sensitivity, leading to false negatives.
Alternative off-line systems are available, which use vacuum to urge gases out of the pack via the any breach. However, these are also typically very slow and so, to maintain production speeds, it is necessary to test multiple packs at a time. This has numerous limitations; there is no way to identify the fault pack when a leak is detected, all packs tested must be rejected. Therefore many “good” packs are lost, increasing operation costs. These systems are often placed later in the packing process, typically when the packs have been collated into large multi-pack cases. This causes further delay in feedback of failures and an error in the packing process may continue to produce “bad” packs for some time. The system size is also much larger and requires more factory space for its operation.
Laser technology has recently been developed which, when provided with an air sample, can accurately and precisely identify, for example, its carbon dioxide content. It has been identified as desirable to incorporate such technology within food packaging production lines as a means of identifying sealed food containers which have breaches by taking a sample of the air surrounding the container after packaging and identifying raised levels of one of the relevant gases relative to standard atmospheric composition. Such laser technology is based on a principle called tunable diode laser absorption spectroscopy (TDLAS), which measures the concentration of species in gaseous mixtures using tunable diode lasers and laser absorption spectrometry. Compared to other measurement techniques, such as paramagnetic detectors (“PMD”) and Chemi-luminescence, TDLAS offers multi-element detection capabilities, high accuracy with a wide dynamic range, low maintenance requirements, and a long life cycle. The use of lasers as spectroscopic light sources allows for high resolution spectroscopy (HRS), with quantum cascade lasers (QCLs) offering access to the valuable mid infrared (MIR) part of the electromagnetic spectrum. An example of a QCL system may be found in WO 03087787 A1.